Re-enable stacktracing when --debug is used

Commit 1f89beb609 introduced the behaviour
that a stacktrace is printed if an exception is encountered.

This helped make the client more supportable:

 $ glance --debug image-list
  .
  .
  .
  File "glanceclient/common/http.py", line 337, in get_http_client
    xxx
 NameError: global name 'xxx' is not defined
 global name 'xxx' is not defined

The behaviour was lost at some point. This patch re-enables it.

Change-Id: I25fc8624797909d606590747f54b9cf649ade079
Closes-bug: 1563830

glanceclient/tests/unit/test_shell.py

@@ -22,6 +22,7 @@ except ImportError:
 import hashlib
 import os
 import sys
+import traceback
 import uuid
 
 import fixtures
@@ -150,6 +151,44 @@ class ShellTest(testutils.TestCase):
         argstr = '--os-image-api-version 2 help foofoo'
         self.assertRaises(exc.CommandError, shell.main, argstr.split())
 
+    @mock.patch('sys.stdout', six.StringIO())
+    @mock.patch('sys.stderr', six.StringIO())
+    @mock.patch('sys.argv', ['glance', 'help', 'foofoo'])
+    def test_no_stacktrace_when_debug_disabled(self):
+        with mock.patch.object(traceback, 'print_exc') as mock_print_exc:
+            try:
+                openstack_shell.main()
+            except SystemExit:
+                pass
+            self.assertFalse(mock_print_exc.called)
+
+    @mock.patch('sys.stdout', six.StringIO())
+    @mock.patch('sys.stderr', six.StringIO())
+    @mock.patch('sys.argv', ['glance', 'help', 'foofoo'])
+    def test_stacktrace_when_debug_enabled_by_env(self):
+        old_environment = os.environ.copy()
+        os.environ = {'GLANCECLIENT_DEBUG': '1'}
+        try:
+            with mock.patch.object(traceback, 'print_exc') as mock_print_exc:
+                try:
+                    openstack_shell.main()
+                except SystemExit:
+                    pass
+                self.assertTrue(mock_print_exc.called)
+        finally:
+            os.environ = old_environment
+
+    @mock.patch('sys.stdout', six.StringIO())
+    @mock.patch('sys.stderr', six.StringIO())
+    @mock.patch('sys.argv', ['glance', '--debug', 'help', 'foofoo'])
+    def test_stacktrace_when_debug_enabled(self):
+        with mock.patch.object(traceback, 'print_exc') as mock_print_exc:
+            try:
+                openstack_shell.main()
+            except SystemExit:
+                pass
+            self.assertTrue(mock_print_exc.called)
+
     def test_help(self):
         shell = openstack_shell.OpenStackImagesShell()
         argstr = '--os-image-api-version 2 help'